Transcript 2nd FEZA School On Zeolites 1
Slide 1
2nd FEZA School On Zeolites
1-2 September 2008 , Paris
X-ray photoelectron spectroscopy
and its use for solid materials
Jacques C. Védrine
Slide 2
General scheme representing
different surface techniques
AES: Auger electron spectroscopy
ISS: Ion scattering
spectroscopy SIMS: Secondary ion mass
spectrometry
ions
electrons
photons
ISS
SIMS
AES
XPS, UPS
XAES
Slide 3
Principle of surface techniques
analyser
source of
photons
ions gun
hn
hn
eions
sample
ions
Slide 4
Electron distribution for a given element: 1s2 2s2 2p6 3s2
Transition time10-7 s; Life time of the hole: 10-5 s
hn = Ek + Eb + Fsp
Slide 5
Scheme of XPS electron level energy
Sample
hn = Ek + Eb + Fsp
Slide 6
XPS spectrum taken at photon energies:
1,486.6 eV (AlKa) and 3,000 eV
O KLL
Ce 3d
AlK
Tb 3d
Ce MNN
a
O 1s
Cu 2p
Tb 4d
Ce 4d
3000 eV
1600
1400
1200
1000
800
Binding energy (eV)
600
400
200
0
Slide 7
Illustrative scheme (left) and VG ESCALAB MkII
spectrometer (right)
Slide 8
Main parameters determined by XPS
1. Binding energy values Eb and chemical shifts DEb
(spin-orbit coupling, final state and multielectronic
effects); Auger peaks
2. Quantitative aspects and surface analysis
3. Case of supported catalysts
4. Applications in heterogeneous catalysis: porous
materials, bimetallic catalysts, organometallic
compounds, mixed oxides materials, basic
catalysts, mixed oxides on CeO2, lanthanide
phosphates, adsorbed species,
Slide 9
Chemical shifts corresponding to different
oxidation states and environments of Al
Ni 3p
J=L+S
Al0
Al 2p
S= ½ L= 0,1,2,3
for s,p,d,f orbitals
Al2O3
spin-orbit coupling varies as Z5
Two components with 2J+1 relative intensities
80
70
60
Slide 10
Chemical shifts observed as a function of oxidation state for several
compounds
EC(A,B) = KC(qA- qB) + VA – VB
KC the overlapping integral between core and valence electrons
qA and qB valence charges of element C in A and B compounds
Element
Electronic
level
Compounds
Chemical shift
/eV
Al
2p
Al0-Al2O3
2.7
Si
2p
Si0-SiO2
4.0
Co
2p3/2
Co0-CoO
Co0-Co3O4
2.1
1.8
Ti
2p3/2
Ti0-TiO
Ti0-Ti2O3
Ti0-TiO2
0.9
3.7
5.1
W
4f7/2
W0-WO2
W0-CrWO4
W0-WO3
1.2
2.6
4.2
Slide 11
XPS Parameters
•
•
•
•
•
•
•
•
initial state Ei with N electrons
final state Ef with N-1 electrons
Eb = EfN-1 - EiN and DEb = DEi - DEf
charge potential model: DEi = (e2r/r) + DV
er charge borne by the element
DV change in potential due to neighbouring atoms (e.g. Madelung potential V= Sj
(qj/Rj) Rj distance between C and atom j bearing a charge qj )
KCq = q/ri, with ri average radius of element C
Final state effects (Koopmans theorem of sudden approximation relaxation) Eib = -ei
+ EiR and DEib = -Dei + DEiR
Multielectronic effects: plasmons, configuration interaction, shake-up and shake-off
processes. npligand nptransition metal difference in energy beween the background state
and the states after photoemission (shake-off if electron ejected in the continuum)
Shake-up peaks for paramagnetic ions as Co2+ (d7), Ni2+ + (d8) or Cu2+ (d9)
Configuration interaction: e.g. Mn2+ d5 ion 6S initial state (Ar 3s23p63d5) and 7S final
state [with two states 7S and 5S depending on the spin orientation] Mn3+ (Ar
3s13p63d5) and energy splitting DE(7S-5S) = [(2S+1)/(2L+1)]G(s,d) [G(s,d) exchange
intergral] and I(7S)/I(5S) = 7/5 as spin-orbit coupling between 2p, 3d, 4f peaks and
(2L+1) /(2S+1) relative peaks intensities.
Slide 12
Principle of the Auger process occurring under photon
or electron impact
e- / photon
e- Auger
e-
Z
Y
X
Ec = E X - EY - EZ
EKL2L3 = EK - EL2 – EL3 – F(L2,L3,X) + R(L2,L3)
Slide 13
Intensity I = P of the emitted beam as a function of its
originating depth x = d from the surface
Slide 14
Universal curve of the electron mean free path
as a function of the electron kinetic energy value
10 eV
100 eV
Slide 15
Quantitative aspects
• dI(q) = F.(NA0/sinq)(ds./d).T.exp(-x/lsinq)dx
∞
∞
• I = I0 ∫0 exp(-xl).d(x) = lI0 [exp(-xl)]0 = lI0
∞
• I(q) = ∫0 F (NA0/sinq)(ds./d).T.exp(-x/lsinq)dx
= FNA0(ds./d).T.l
• NA/NB = (IA/IB)(sB/sA)(TB/TA)(lB/lA)
• (ds/d ).(q,hn) = (s/4p) [1+ (b/2).{(3sin2a)/2)-1}]
• NA/NB = (IA/IB).[sB (EkB)x] / [sA (EkA)x] .TB/TA
with x = 0.5 to 0.75
Slide 16
Scheme of a supported catalyst of high surface area support as proposed
by Kerkhof et al
(Ip/Is)exp = (Np/Ns)b (sp/ss){ [1+ exp(-ds/2ls)] / [1-exp(-ds/2ls)]}{[1-exp(-dp/l p)]
/ (dp/lp}} ds = 2/S.r
1
Support
Promoter
2
j
Ip/IS = (NS/Np).(sp/ss).(ds/2l)
Approx.:
catalyst particle =
infinite number of
sheets
high surface area
Slide 17
Ip/IS = (NS/Np).(sp/ss).F(d,lp)
• F(d,lp) = (3/2).{1-(2lp2/d2)[1-exp(-d/lp)]+ (2
lp/d) exp(-d/lp)} for spherical crystallites of
diameter d
• F(d,lp) = 3{[1-(8lp2/d2)].[1-exp(-d/2lp)] +
(4lp/d) exp(-d/2lp)} for hemispherical
crystallites of diameter d
• F(d,lp) = 1-exp(-d/lp) for cubic or planar
deposits of thickness d
Slide 18
Prediction and experimental metal dispersion for Pt/SiO2
catalysts
0,35
monolayer
0,3
IPt/ISi
monolayer
I Pt/I Si exptl
0,25
0,2
0,15
0,1
0,05
0
0,0E+00
5,0E-03
1,0E-02
Pt/Si bulk
1,5E-02
Slide 19
Schematic models for supported catalysts
1
1
1
2
2
2
3
3
3
a) Layer mode
b) Island mode
c) Layer + island
(Frank-van der
Merwe, 2 D)
(Volmer-Weber, 3 D)
mode
(StranskiKrastanov)
(a)
IS
d
exp
IS0
l
(f = 0.5)
(b)
IS
d
1 f f exp i
IS0
l
(c)
IS
d
dm
exp _ 1 f f exp i
IS0
l
l
Slide 20
IS /IS 0
Theoretical calculated XPS peak intensity ratio
variations for supported catalysts. Case of Cu/MgO
1,2
1
0,8
0,6
0,4
0,2
0
model a
model b
model c
IS /IS 0
0
5
10
1,2
1
0,8
0,6
0,4
0,2
0
15
mean coverage (Å)
model a
model b
model c
Cu/M gO
0
5
10
15
mean coverage (Å)
Slide 21
Ag 3d XPS spectra of 0.3Pd-0.6Ag/pumice catalyst in a)
as synthesised; b) oxidised at 623K; c) reduced at 623K
Slide 22
Spectra of MgNd alloys (25wt% Nd) oxidised for 90 min at 773K
Slide 23
O1s, Eu 3d5/2 and Eu 4d XPS spectra of EuIII
organometallic compounds
Slide 24
Binding energy values in eV of Eu3d5/2 peaks and of its associated
shake-down satellite and ratio of intensities for EuIIIcompounds
EuIIIcompounds
Eu2O3
Eu2 (C2O4)3
Eu(acac)3
Eu2 (CO3)3
Eu2 (SO4)3
Eu(NO3)3
Eb Eu3d5/2
Eb shake down satellite
DEb
1133.7
1133.9
1135.0
1135.3
1135.9
1136.4
1123.5
1124.0
1124.9
1125.2
1125.7
1126.0
10.2
9.9
10.1
10.1
10.2
10.4
For europium 4f65d1and 4f75d0 configurations in the final state
unoccupied 4f levels are lowered in energy by the potential of the
created photohole (Coulomb interaction of the created photohole
with the electron system)
Slide 25
Correlation between Pauling electronegativity of the heteroatom X
and O1s binding energy values for EuIII compounds
Slide 26
Basic oxide catalysts used for propane ODH to propene
Rare earth element Mg, Ca, Sr doped with Nd (5 mol% Nd2O3)
(Nd 3d (left) and Nd 4d (right) core levels from the Nd/CaO
sample; insert: Nd 3d5/2 peak decomposition
34000
Nd 3d3/2
Nd 3d5/2
26000
29000
O KLL Auger line
25000
21000
990
985
980
975
970
965
Intensity (arb. units)
33000
22000
18000
800
600
400
200
145
10000
1000
1000
14000
17000
960
Binding energy (eV)
1020
1200
980
Binding energy (eV)
960
140
135
130
125
Binding energy (eV)
120
115
0
110
Intensity (arb. units)
Nd 3d 5/2
Intensity (arb. units)
30000
Slide 27
Nd content as determined from chemical analysis and XPS
Nd 3d or Nd 4d, M* = Mg 1s, Ca 2p, Sr 3d peak intensities
Catalysts
Nd/M*
Chem Anal.
Nd/M*
XPS
Excess of
Nd on the
surface (at %)
Nd/MgO
0.10
0.17 ± 0.04
5.4
Nd/CaO
0.09
0.14 ± 0.02
4.0
Nd/SrO
0.10
0.13 ± 0.02
2.4
slight enrichment (<5%) of the surface with Nd with respect to the bulk
Slide 28
XPS spectra before catalytic testing and their
decomposition: Nd/MgO (a), Nd/CaO (b), Nd/SrO (c)
55000
23000
19000
15000
11000
538
536
534
532
530
Binding energy (eV)
Intensity (CPS)
a
b
25000
15000
7000
526
528
35000
538
536
534
532
530
528
5000
526
Binding energy (eV)
7000
5000
3000
538
536
534
532
530
528
Intensity (eV)
cc
1000
526
Binding energy (eV)
O1s in oxide (Eb ~ 530.0 eV), in adsorbed water Eb ~ 534.0 eV and from
hydroxyls and carbonates (Eb ~ 532.0 eV),
Intensity (CPS)
45000
Slide 29
C1s XPS peaks before catalytic testing and their
decomposition: Nd/MgO (a), Nd/CaO (b), Nd/SrO (c)
13000
5500
Carbonate
295
290
2500
b
Carbonate
1000
280
295
Carbonate
285
Binding energy (eV)
5000
290
3500
Carbonate
1500
280
270
Intensity (CPS)
Sr 2p1/2
2500
290
285
1000
280
Binding energy (eV)
Sr 2p3/2
c
9000
Intensity (CPS)
4000
Intensity (CPS)
a
500
260
Binding energy (eV)
C1s peaks at ~ 285 eV for contamination carbon (adventitious hydrocarbon
species) and ~ 290.0 eV for carbonates
Slide 30
Mixed oxides based on CeO2
Ce 3d experimental spectrum and its decomposition
Final state effect: v (u)
v’’(u’’):
Multiplet splitting: v’’’(u’’’):
vo(uo):
v’(u’):
u’’’
v’’’
u
u’’
CeIV : 3d95d6s0 4f1-O2p5
CeIV : 3d95d6s0 4f2-O2p4
CeIV : 3d95d6s0 4f0-O2p6
CeIII : 3d95d6s0 4f1-O2p6
CeII : 3d9 5d6s0 4f2-O2p5
v
u’
v’
v’’
910
900
890
918
908
898
880
v0
870
888
878
Binding Energy (eV)
Slide 31
Concluding remarks
• XPS is the most currently used « surface » technique
• Quantitative data are determining but should be used
with care, unless the geometry of particles and
support are well known
• Not really useful for porous materials as too sensitive
to the surface (1-5nm) of particles usually in mm-mm
size range
• Chemical shifts and multiplet peaks are useful
« chemical » indications
• Challenges for analysis under « pressure » and for
spatial resolution and scanning analysis
2nd FEZA School On Zeolites
1-2 September 2008 , Paris
X-ray photoelectron spectroscopy
and its use for solid materials
Jacques C. Védrine
Slide 2
General scheme representing
different surface techniques
AES: Auger electron spectroscopy
ISS: Ion scattering
spectroscopy SIMS: Secondary ion mass
spectrometry
ions
electrons
photons
ISS
SIMS
AES
XPS, UPS
XAES
Slide 3
Principle of surface techniques
analyser
source of
photons
ions gun
hn
hn
eions
sample
ions
Slide 4
Electron distribution for a given element: 1s2 2s2 2p6 3s2
Transition time10-7 s; Life time of the hole: 10-5 s
hn = Ek + Eb + Fsp
Slide 5
Scheme of XPS electron level energy
Sample
hn = Ek + Eb + Fsp
Slide 6
XPS spectrum taken at photon energies:
1,486.6 eV (AlKa) and 3,000 eV
O KLL
Ce 3d
AlK
Tb 3d
Ce MNN
a
O 1s
Cu 2p
Tb 4d
Ce 4d
3000 eV
1600
1400
1200
1000
800
Binding energy (eV)
600
400
200
0
Slide 7
Illustrative scheme (left) and VG ESCALAB MkII
spectrometer (right)
Slide 8
Main parameters determined by XPS
1. Binding energy values Eb and chemical shifts DEb
(spin-orbit coupling, final state and multielectronic
effects); Auger peaks
2. Quantitative aspects and surface analysis
3. Case of supported catalysts
4. Applications in heterogeneous catalysis: porous
materials, bimetallic catalysts, organometallic
compounds, mixed oxides materials, basic
catalysts, mixed oxides on CeO2, lanthanide
phosphates, adsorbed species,
Slide 9
Chemical shifts corresponding to different
oxidation states and environments of Al
Ni 3p
J=L+S
Al0
Al 2p
S= ½ L= 0,1,2,3
for s,p,d,f orbitals
Al2O3
spin-orbit coupling varies as Z5
Two components with 2J+1 relative intensities
80
70
60
Slide 10
Chemical shifts observed as a function of oxidation state for several
compounds
EC(A,B) = KC(qA- qB) + VA – VB
KC the overlapping integral between core and valence electrons
qA and qB valence charges of element C in A and B compounds
Element
Electronic
level
Compounds
Chemical shift
/eV
Al
2p
Al0-Al2O3
2.7
Si
2p
Si0-SiO2
4.0
Co
2p3/2
Co0-CoO
Co0-Co3O4
2.1
1.8
Ti
2p3/2
Ti0-TiO
Ti0-Ti2O3
Ti0-TiO2
0.9
3.7
5.1
W
4f7/2
W0-WO2
W0-CrWO4
W0-WO3
1.2
2.6
4.2
Slide 11
XPS Parameters
•
•
•
•
•
•
•
•
initial state Ei with N electrons
final state Ef with N-1 electrons
Eb = EfN-1 - EiN and DEb = DEi - DEf
charge potential model: DEi = (e2r/r) + DV
er charge borne by the element
DV change in potential due to neighbouring atoms (e.g. Madelung potential V= Sj
(qj/Rj) Rj distance between C and atom j bearing a charge qj )
KCq = q/ri, with ri average radius of element C
Final state effects (Koopmans theorem of sudden approximation relaxation) Eib = -ei
+ EiR and DEib = -Dei + DEiR
Multielectronic effects: plasmons, configuration interaction, shake-up and shake-off
processes. npligand nptransition metal difference in energy beween the background state
and the states after photoemission (shake-off if electron ejected in the continuum)
Shake-up peaks for paramagnetic ions as Co2+ (d7), Ni2+ + (d8) or Cu2+ (d9)
Configuration interaction: e.g. Mn2+ d5 ion 6S initial state (Ar 3s23p63d5) and 7S final
state [with two states 7S and 5S depending on the spin orientation] Mn3+ (Ar
3s13p63d5) and energy splitting DE(7S-5S) = [(2S+1)/(2L+1)]G(s,d) [G(s,d) exchange
intergral] and I(7S)/I(5S) = 7/5 as spin-orbit coupling between 2p, 3d, 4f peaks and
(2L+1) /(2S+1) relative peaks intensities.
Slide 12
Principle of the Auger process occurring under photon
or electron impact
e- / photon
e- Auger
e-
Z
Y
X
Ec = E X - EY - EZ
EKL2L3 = EK - EL2 – EL3 – F(L2,L3,X) + R(L2,L3)
Slide 13
Intensity I = P of the emitted beam as a function of its
originating depth x = d from the surface
Slide 14
Universal curve of the electron mean free path
as a function of the electron kinetic energy value
10 eV
100 eV
Slide 15
Quantitative aspects
• dI(q) = F.(NA0/sinq)(ds./d).T.exp(-x/lsinq)dx
∞
∞
• I = I0 ∫0 exp(-xl).d(x) = lI0 [exp(-xl)]0 = lI0
∞
• I(q) = ∫0 F (NA0/sinq)(ds./d).T.exp(-x/lsinq)dx
= FNA0(ds./d).T.l
• NA/NB = (IA/IB)(sB/sA)(TB/TA)(lB/lA)
• (ds/d ).(q,hn) = (s/4p) [1+ (b/2).{(3sin2a)/2)-1}]
• NA/NB = (IA/IB).[sB (EkB)x] / [sA (EkA)x] .TB/TA
with x = 0.5 to 0.75
Slide 16
Scheme of a supported catalyst of high surface area support as proposed
by Kerkhof et al
(Ip/Is)exp = (Np/Ns)b (sp/ss){ [1+ exp(-ds/2ls)] / [1-exp(-ds/2ls)]}{[1-exp(-dp/l p)]
/ (dp/lp}} ds = 2/S.r
1
Support
Promoter
2
j
Ip/IS = (NS/Np).(sp/ss).(ds/2l)
Approx.:
catalyst particle =
infinite number of
sheets
high surface area
Slide 17
Ip/IS = (NS/Np).(sp/ss).F(d,lp)
• F(d,lp) = (3/2).{1-(2lp2/d2)[1-exp(-d/lp)]+ (2
lp/d) exp(-d/lp)} for spherical crystallites of
diameter d
• F(d,lp) = 3{[1-(8lp2/d2)].[1-exp(-d/2lp)] +
(4lp/d) exp(-d/2lp)} for hemispherical
crystallites of diameter d
• F(d,lp) = 1-exp(-d/lp) for cubic or planar
deposits of thickness d
Slide 18
Prediction and experimental metal dispersion for Pt/SiO2
catalysts
0,35
monolayer
0,3
IPt/ISi
monolayer
I Pt/I Si exptl
0,25
0,2
0,15
0,1
0,05
0
0,0E+00
5,0E-03
1,0E-02
Pt/Si bulk
1,5E-02
Slide 19
Schematic models for supported catalysts
1
1
1
2
2
2
3
3
3
a) Layer mode
b) Island mode
c) Layer + island
(Frank-van der
Merwe, 2 D)
(Volmer-Weber, 3 D)
mode
(StranskiKrastanov)
(a)
IS
d
exp
IS0
l
(f = 0.5)
(b)
IS
d
1 f f exp i
IS0
l
(c)
IS
d
dm
exp _ 1 f f exp i
IS0
l
l
Slide 20
IS /IS 0
Theoretical calculated XPS peak intensity ratio
variations for supported catalysts. Case of Cu/MgO
1,2
1
0,8
0,6
0,4
0,2
0
model a
model b
model c
IS /IS 0
0
5
10
1,2
1
0,8
0,6
0,4
0,2
0
15
mean coverage (Å)
model a
model b
model c
Cu/M gO
0
5
10
15
mean coverage (Å)
Slide 21
Ag 3d XPS spectra of 0.3Pd-0.6Ag/pumice catalyst in a)
as synthesised; b) oxidised at 623K; c) reduced at 623K
Slide 22
Spectra of MgNd alloys (25wt% Nd) oxidised for 90 min at 773K
Slide 23
O1s, Eu 3d5/2 and Eu 4d XPS spectra of EuIII
organometallic compounds
Slide 24
Binding energy values in eV of Eu3d5/2 peaks and of its associated
shake-down satellite and ratio of intensities for EuIIIcompounds
EuIIIcompounds
Eu2O3
Eu2 (C2O4)3
Eu(acac)3
Eu2 (CO3)3
Eu2 (SO4)3
Eu(NO3)3
Eb Eu3d5/2
Eb shake down satellite
DEb
1133.7
1133.9
1135.0
1135.3
1135.9
1136.4
1123.5
1124.0
1124.9
1125.2
1125.7
1126.0
10.2
9.9
10.1
10.1
10.2
10.4
For europium 4f65d1and 4f75d0 configurations in the final state
unoccupied 4f levels are lowered in energy by the potential of the
created photohole (Coulomb interaction of the created photohole
with the electron system)
Slide 25
Correlation between Pauling electronegativity of the heteroatom X
and O1s binding energy values for EuIII compounds
Slide 26
Basic oxide catalysts used for propane ODH to propene
Rare earth element Mg, Ca, Sr doped with Nd (5 mol% Nd2O3)
(Nd 3d (left) and Nd 4d (right) core levels from the Nd/CaO
sample; insert: Nd 3d5/2 peak decomposition
34000
Nd 3d3/2
Nd 3d5/2
26000
29000
O KLL Auger line
25000
21000
990
985
980
975
970
965
Intensity (arb. units)
33000
22000
18000
800
600
400
200
145
10000
1000
1000
14000
17000
960
Binding energy (eV)
1020
1200
980
Binding energy (eV)
960
140
135
130
125
Binding energy (eV)
120
115
0
110
Intensity (arb. units)
Nd 3d 5/2
Intensity (arb. units)
30000
Slide 27
Nd content as determined from chemical analysis and XPS
Nd 3d or Nd 4d, M* = Mg 1s, Ca 2p, Sr 3d peak intensities
Catalysts
Nd/M*
Chem Anal.
Nd/M*
XPS
Excess of
Nd on the
surface (at %)
Nd/MgO
0.10
0.17 ± 0.04
5.4
Nd/CaO
0.09
0.14 ± 0.02
4.0
Nd/SrO
0.10
0.13 ± 0.02
2.4
slight enrichment (<5%) of the surface with Nd with respect to the bulk
Slide 28
XPS spectra before catalytic testing and their
decomposition: Nd/MgO (a), Nd/CaO (b), Nd/SrO (c)
55000
23000
19000
15000
11000
538
536
534
532
530
Binding energy (eV)
Intensity (CPS)
a
b
25000
15000
7000
526
528
35000
538
536
534
532
530
528
5000
526
Binding energy (eV)
7000
5000
3000
538
536
534
532
530
528
Intensity (eV)
cc
1000
526
Binding energy (eV)
O1s in oxide (Eb ~ 530.0 eV), in adsorbed water Eb ~ 534.0 eV and from
hydroxyls and carbonates (Eb ~ 532.0 eV),
Intensity (CPS)
45000
Slide 29
C1s XPS peaks before catalytic testing and their
decomposition: Nd/MgO (a), Nd/CaO (b), Nd/SrO (c)
13000
5500
Carbonate
295
290
2500
b
Carbonate
1000
280
295
Carbonate
285
Binding energy (eV)
5000
290
3500
Carbonate
1500
280
270
Intensity (CPS)
Sr 2p1/2
2500
290
285
1000
280
Binding energy (eV)
Sr 2p3/2
c
9000
Intensity (CPS)
4000
Intensity (CPS)
a
500
260
Binding energy (eV)
C1s peaks at ~ 285 eV for contamination carbon (adventitious hydrocarbon
species) and ~ 290.0 eV for carbonates
Slide 30
Mixed oxides based on CeO2
Ce 3d experimental spectrum and its decomposition
Final state effect: v (u)
v’’(u’’):
Multiplet splitting: v’’’(u’’’):
vo(uo):
v’(u’):
u’’’
v’’’
u
u’’
CeIV : 3d95d6s0 4f1-O2p5
CeIV : 3d95d6s0 4f2-O2p4
CeIV : 3d95d6s0 4f0-O2p6
CeIII : 3d95d6s0 4f1-O2p6
CeII : 3d9 5d6s0 4f2-O2p5
v
u’
v’
v’’
910
900
890
918
908
898
880
v0
870
888
878
Binding Energy (eV)
Slide 31
Concluding remarks
• XPS is the most currently used « surface » technique
• Quantitative data are determining but should be used
with care, unless the geometry of particles and
support are well known
• Not really useful for porous materials as too sensitive
to the surface (1-5nm) of particles usually in mm-mm
size range
• Chemical shifts and multiplet peaks are useful
« chemical » indications
• Challenges for analysis under « pressure » and for
spatial resolution and scanning analysis